Constant temperature bath



NOV 2, 1965 M. R. CANNON ETAL 3,214,937

CONSTANT TEMPERATURE BATH Filed Feb. 2e, 196s INVENTORS United StatesPatent O 3,214,937 CONSTANT TEh/IPERATURE BATH Michael R. Cannon,deceased, late of Boalsbnrg, Pa., by

Elizabeth L. Cannon, executrix, and Robert E. Manning, Boalsburg, andWallis A. Lloyd, State College, Pa., assignors to Cannon InstrumentCompany, Bealsburg, Pa., a corporation of Pennsylvania Filed Feb. 26,1963, Ser. No. 261,174 12 Claims. (Cl. 62--38-i) This invention relatesto a constant, low temperature bath useful for conducting experiments,such as viscosity measurements, at a low temperature which is closelycontrolled within narrow limits.

The need for a dependable laboratory bath of this kind is growing, owingto the increasing interest in the behavior and utility of lubricants,fuels, hydraulic fluids, and the like at low temperatures. For example,military installations in arctic climates have generated an everwidening investigation of the viscosity behavior of lubricants and otheruids at reduced temperatures, and as a natural consequence, considerableattention has been devoted to instruments and apparatus for measuringviscosity at .these temperatures. While conventional refrigerationequipment can be used to hold a test material at low temperature, ittends to be quite bulky and to require valuable laboratory or otherspace usually ill spared. Furthermore, such equipment is complicated toinstall and operate, entails high initial costs, and is apt to requireexpert maintenance.

By contrast, the invention provides a cooling device which, in respectof the foregoing, is in sharp contrast to conventional equipment, andwhich avoids the disadvantages described. The device is of desirablesimplicity, and has proved to be sound. It comprises generally a bathliquid which is to be maintained at a constant low temperature, acontainer for the liquid, a member of heat conducting material extendinginto the liquid in heat exchange relation therewith, and, incommunication with the member, a reservoir of coolant or heat transfermedium adapted to flow into the member to cool down the bath liquid.Suitably the member is connected to the door of the reservoir, whichenables the cooling medium to ow by gravity into the member, the latterbeing closed at its lower end. While a number of coolants are suitable,commercial Dry Ice, or frozen carbon dioxide, is admirable, and theinvention may be described in detail in connection with this material.The Dry Ice is placed in chunks in the reservoir together with a smallamount of a solvent therefor. Cooled sol` vent, ltogether with somedissolved Dry Ice, flow into and ll the member, and the latter acts tocool the bath liquid by heat exchange. Heat abstracted from the bathboils out dissolved carbon dioxide from the solvent, which flowsupwardly in the member to the reservoir, pushing upward some solventsomewhat depleted in dissolved carbon dioxide, and the member is thenautomatically refilled by cold solvent from the reservoir. In this waythe temperature of the bath liquid may be brought down to a desired lowtemperature, at which point the flow of cold solvent into the member isreduced, and a fine control temperature-regulating system is actuated tomaintain the temperature.

The invention may be better understood by referring to the accompanyingdrawings, which are diagrammatic, and in which FIG. l is a perspectiveview of the constant temperature device, with portions being brokenaway;

FIG. la is a simplified circuit diagram of the heater and controlcircuit;

li? Patented Nov. 2, 1965 FIG. 2 is a fragmental view looking in thedirection of arrow A in FIG. l; and

FIGS. 3 and 4 are views like FIG. 2 but showing modifications.

Referring to FIG. 1, the constant temperature device comprises acontainer 10 supported by means not shown in a cabinet 11 which enclosesthe container on all sides. The container, which is in the form of anopen top glass Dewar cylinder, although it may have any other suitableform, is disposed in the forepart of the cabinet and is covered by a lid12 which proivdes a working area for placing test equipment in thecontainer. The latter is nearly filled with bath liquid 13 comprisingthe liquid which is to be cooled and maintained at constant temperature.Back of lid 12, and resting on the back part of cabinet 11, is areservoir 14 comprising a thick-walled tank for holding coolant,Suitably the tank has inner and outer walls 15 and 16 of metal betweenwhich is a thick layer of insulation 17. The floor 1S of the tank issimilarly constructed, as is the lid 19, shown exploded and partially insection. The lid may engage the tank through hinges (not shown).

The coolant in reservoir 14 comprises chunks or blocks 2l) of Dry Ice,the lower blocks of which are partially immersed in a Dry Ice solvent 21such as methanol or acetone. The blocks rest on a screen 22 which isdisposed a small distance above oor 18, say 1A; to 1 inch, preferably1/2 to 3%: inch, and thus solvent has free access to the blocks. Thelevel of solvent in the tank may be up to about 6 inches, preferablyabout 5%: to 2 inches.

In the forward part of tank 14 where it overlaps the Dewar vessel 10, amember 23, preferably in the form of a hollow tube, extends downwardlyfrom the oor of the tank into the bath liquid 13. Tube 23 may, but notnecessarily, project above the tank oor a short distance, identified as24, which is less than the depth of solvent 21, to insure that therewill be a constant ow of solvent into the tube. The latter extendsthrough the floor insulation at 25, and suitably may have a press orweld t with the door in order to be supported thereby.

Flow of solvent plus dissolved carbon dioxide into tube 23 is suitablycontrolled by a valve arrangement such as that shown in FIG. l2comprising a plug 30 of a generally suitable shape, such ashernispherical, or conical, or some other tapered, or even flat contour.As shown, the plug is hemispherical and is adapted to seat on the upperend 24 of the tube, the latter being suitably bevelled or concaved, asat 3l., to receive the plug. The plug is attached to and moved by therod 32, which at its upper end 33 is energized by cam 34 connected bypin 35 to manually operated knob 36 on the outer surface 37 of wall 38of the tank. Pin 35 extends through the wail. The rod 32 is supported byright-angled bearing brackets 39 and Kill. A coil spring 41 engages therod, and at its lower end bears on the shelf 42; `of bracket di) whileits upper end engages a retainer 43 xedly secured to the rod. The springthus biases the rod against the cam.

Forwardly of tank 14, the lid or working area 12 is provided with anumber of openings 44 for receiving conventional instrument-holdingStoppers 4S. The latter have suitable openings (not shown) for theinstruments. One stopper may be used to hold a conventionalthermoregulator 46, shown with a length of lead connected thereto andcomprising a temperature-controlled switch which operates a conventionalrelay (not shown) to turn on or shut off an electric heater showndiagrammatically at 47. The heater 47 is disposed in the bath liquid 13.This arrangement, which is conventional, is illustrated by thesimplified circuit diagram in FIG. la comprising the heater 47 connectedon one side to the power source 48 and on the other side to the relay49. Thermoregulator switch 46 connects the relay coil 49a to the powersource. A stirrer (not shown) helps keep the bath liquid in temperatureequilibrium, as is conventional, and a Window 50 in front panel 51 ofthe cabinet 11 enables the operator to watch the progress of the tests.A fluorescent light (not shown) is located below the window inside thehousing to provide good visibility. Also, a circular electric heater(not shown) is located in the annular air space between housing orcabinet 11 and container 10, and adjacent the lower end of thecontainer, in order to prevent frosting and water condensation on thewindow and the outer surfaces of the container.

To operate the device, Dry Ice in large chunks, say 1 to 5 or l0 incheson a side, is placed in the tank and sucient solvent added to overflowinto and ll the tube 23. The Dry Ice quickly cools the solvent to a lowtemperature; for example, with acetone the temperature is rapidlydecreased to below 100 F. within a few minutes. Cooled solvent plusdissolved carbon dioxide, hereinafter referred to as solution, flowsdown into the tube 23, displacing the warmer liquid, and creating acycle which repeats itself over and over. As cooled solution flows intotube 23, thermal convection currents are set up immediately, and thebath liquid, which normally is mechanically stirred, proceeds to coolrapidly. The tube transfers heat rapidly not only because of theseconvection currents but also because dissolved carbon dioxide is boiledout of the solution inside the tube. As a result, solution flows orgushes rapidly out of the tube as it becomes warmer through abstractionof heat from the bath liquid, and colder solution from the tankimmediately replaces the same. This cycle repeats itself automatically.Gaseous carbon dioxide may be vented to hood or outdoors through tube54, to which rubber or other exible tubing is connected.

When the bath is near the desired temperature, the valve plug 30 ismoved to partially close tube 23 by rotating knob 36. This reduces theflow in tube 23 and decreases the rate of cooling. After furtheradjustment of the valve as may be necessary, line control of the bathtemperature is provided by the electric heater 47 in response to thethermoregulator 46.

During the conduct of tests, such as viscosity tests, it is desirable tohave over-cooling capacity so that when test instruments are immersed inthe bath the heat imparted to it will not increase its temperatureundesirably. Over-cooling may be accomplished by further opening tube 23by the valve 30.

A modified heat transfer member is shown in FIG. 3 wherein a tube 52 ofsmaller diameter is disposed within and concentric to tube 23a of largerdiameter, creating an annular space 53. Tube 52 is open at both ends andterminates within an inch or two of the bottom of tube 23a. The latteris closed olf at the bottom. Both tubes at their upper ends open in thesame plane and may be closed off by a plug valve 30a having a at lowerface 53 which covers both tube openings. In this modification, coldliquid initially lls both tubes, and as the liquid is warmed by the bathliquid in the process of abstracting heat therefrom, carbon dioxide gasows upwardly in the small tube. An advantage of this arrangement is thatthe ow of gas up and cold liquid down tends to be more rapid since eachhas its own path, so to speak. Thus less time is required for the bathto cool from room to test temperature.

In the modification of FIG. 4, two heat transfer members are againemployed, a smaller and a larger one, but the smaller one, comprisingthe tube 60, is disposed to one side of the larger tube 23b. The plugvalve 30b seals off only the tube 23h, as in FIG. 2. The tube 60 is openat the top and closed at the bottom. After the bath liquid has attainedconstant temperature, the heat transfer rate is much smaller than it isduring the cooling-down period, and consequently the larger tube can beclosed and the smaller one kept in operation as needed to maintain thedesired temperature. If desired, a valve, shown in dotted outline as30e, may be used with the smaller tube for fine control, the valvearrangement being just like that for the larger tube but appropriatelyscaled down 1n s1ze.

The desired low temperature of the bath will depend in part on thesolvent, but with this in mind, a wide range of temperatures isavailable, extending for example from just below room temperature downto about F. The bath liquid 13, of course, is one that is liquid andstable at the chosen temperature, and may include waxfree hydrocarbons,acetone, methanol, etc. If desired, the bath liquid may be the same asthe carbon dioxide solvent, described below.

Accurate control over the bath test temperature is possible, thevariation being less than plus or minus 0.04 F. at bath temperature of 0to -65 F., and in many cases the variation being no more than plus orminus 0.01 F. For bath temperatures between room and 0 F. the variationmay be less than 0.02 F.

The carbon dioxide solvent may suitably be chosen from low molecularweight compounds including alcohols, ketones, ethers, esters, aldehydes,organic acids, etc. Low molecular weight compounds are desirablebecause, in general, their viscosity is loW and they flow easily at thelow temperatures involved. Illustrative specific solvents are methanol,ethanol, propanol, isopropanol, n-butanol, isobutanol, acetone, methylethyl ketone, methyl acetate, ethyl acetate, methyl butyrate,acetaldehyde, propionaldehyde. Other compounds are normal andiso-hexanes and pentanes.

The position of the Dry Ice tank 14 relative to the bath holder 10 is aconvenient one and permits gravity ow of the Dry Ice solution in theheat transfer member 23. It will be understood in this connection thatthe tank may have other positions relative to the bath liquid or holderand that forced ow of the Dry Ice solution may be employed. Also, themember 23 need not necessarily extend from the oor of the tank, althoughthat is a preferred arrangement; if need be, it can be operativelyconnected to the tank through a side or end wall, or the top. Thismember is shown as circular in cross section, but may have any suitablecross-sectional shape, such as a square, triangular, rectangular,pentagonal, hexagonal, or other multi-sided shape, including a starshape of any number of points, and further including curved as well asangular shapes. It will be appreciated, in this connection, that therate of heat transfer increases with increasing surface area, all otherthings being the same. Any suitable material may be used to constructthe heat transfer member, due care being `observed to select a materialof suitable strength and durability as well as heat transfer capability.Stainless steel is satisfactory, as yis brass, aluminum, copper, nickel,zinc, iron, titanium, molybdenum, etc.

EXAMPLE A cooling device constructed substantially in the mannerillustrated in FIG. 1 had as bath holder a Pyrex glass Dewar or about l2inches inside diameter and 16 inches depth, and a Dry Ice tank ofstainless steel measuring 13 inches by ll inches by 11 inches and having2 inches of insulation on all sides, including top and bottom. Athin-walled stainless steel, cylindrical heat transfer tube of 2 inchesoutside diameter and 13 inches length was xedly secured to the bottom ofthe tank, with the opening of the tube controlled by a spring-loadedcamoperated hemispherical plug valve that was movable by turning a knobon the front side of the tank, substantially as shown in FIG. 2. Aconventional electric heater, theremoregulator, and stirrer wereinstalled to operate in the Dewar, and the heater and thermoregulatorconnected in series with a relay and a main A.C. supply. Thethermoregulator (a thermometer incorporating a switch) actuated therelay, which turned the heater on or oit. The stirrer was connecteddirectly to the main supply.

About 6 gallons of acetone were placed in the glass Dewar. Chunks of DryIce were placed on a screen on the tank Hoor, and the latter illed to adepth of about 2 inches with acetone, after rst filling the tube. Themouth of the tube was below the level of the acetone in the tank.Movement into the tube of acetone containing dissolved carbon dioxidebegan almost immediately, with warmer acetone in the tube beingdisplaced. Beginning with the bath liquid at room temperature,temperature measurements of the bath were made at short intervals andare recorded below. Two such runs were made, each on diierent days.

Run l:

Time, p m. Temp. F. 1:23 63 Time, pm. Temp F. 1:29 66 It will be seenthat rapid cooling rates were obtained, in each case the bath going fromroom temperature to 65 F. in less than an hour. It may be noted that astandard low test temperature currently in luse is 60 F.

Besides Dry Ice, other useful coolants are liquid carbon dioxide, liquidhelium, liquid air, liquid oxygen, liquid nitrogen, liquid argon and, infact, any other normally gaseous material which can be liquied at asuitably low temperature, including the Freons (a group of halogenatedhydrocarbons containing one or more uorine atoms). Liquid carbon dioxideunder pressure is suitable. The liquid coolants may be used with orwithout a solvent.

Other temperature sensing devices may be substituted for thethermoregulator, such as a resistance thermometer, thermister, gasthermometer, bi-metallic strip, etc., each controlling through a relay,or a magnetic amplier, or directly, the current through the immersionheater. Ir desired, the immersion heater may be omitted if the openingof the valve 30-31 is automatically controlled by the temperaturesensing device.

It is apparent that the Dry Ice tank and the heat transfer memberassociated therewith are adaptable for use with many existing constanttemperature baths, that is, baths normally operated at hightemperatures, such as 100 F. or 210 F., and that these baths may therebybe converted to constant low temperature baths without diculty.

It may now be seen that the invention makes lavailable a compact bath ofsimple construction which takes up little space and which is easy tooperate. It is capable of rapidly attaining test temperatures. Afteruse, or during overnight periods, it may be shut oit, and laterrestarted without diiculty and without an unduly large waiting period.

It will be understood that the invention is capable of obviousvariations without departing from its scope.

In the light of the foregoing description, the following is claimed:

1. A constant low temperature bath comprising a bath liquid which is tobe maintained at a constant temperature below room temperature, a hollowmember of heat conducting material extending into the bath liquid inheat exchange relationship therewith, a reservoir for a coolant incommunication with the member, said coolant being adapted to ilow fromthe reservoir into the member and thereby cool the bath liquid, means toreduce the ilow in the member, and means in the bath liquid independentof the member for assisting to maintain the bath liquid at said constantlow temperature.

2. A constant low temperature bath comprising a bath liquid which is tobe maintained at a constant temperature below room temperature, a tubeof heat conducting material extending into the bath liquid in heatexchange relationship therewith, a reservoir of Ia low boiling carbondioxide solvent adjacent the upper end of the tube, said upper tube endbeing in c-ommunication with the solvent, a mass of solid carbon dioxideresting in the solvent and serving to cool the same, said cooled solventbeing adapted to iiow by gravity from the reservoir into the tube andthereby cool the bath liquid, the heat of the bath liquid acting to boilout dis solved carbon dioxide from the solvent and said tube conductingthe resulting carbon dioxide gas to Said reservoir, said tube in turnbeing refilled by colder solvent from the reservoir, means to reduce theow into and out of the tube, and means in the bath liquid independent ofthe tube for helping to maintain the bath liquid at said constant lowtemperature.

3. A constant low temperature bath comprising a bath liquid, a containerof cold heat transfer medium in the non-gaseous phase adjacent said bathliquid, said medium being a gas at bath temperatures, a supply ofSolvent for said medium in contact therewith and forming a solution ofthe same on the floor of the container, a heat transfer member extendingfrom the container into the bath liquid and having means for permittingflow of said solution therein, the solution in the container beingadapted to ow in said member to cool down the bath liquid by heatexchange therewith, means for venting gaseous medium from the container,means for reducing the flow of solution into the member, and a secondheat transfer member extending from the container into the bath liquid.

4. The bath of claim 3 wherein said second member is concentricallydisposed within the first member.

5. The bath of claim 3 wherein said second member is separate from anddisposed laterally of the first member.

6. In a constant temperature bath comprising a bath liquid, theimprovement comprising a tank for Dry Ice adjacent said bath, a supplyof solvent or Dry Ice in contact therewith and forming a Dry Icesolution in the floor of the tank, a hollow heat transfer memberextending from the tank into the bath liquid, said member having an openend portion which extends just above said tank floor and which receivessolution only from adjacent the tank floor, said member having a closedend portion disposed in and terminating in the bath liquid, the solutionin the tank being adapted to flow in said member and to cool down thebath liquid by heat exchange therewith, said solution being out ofContact with the bath liquid, the heat of the bath acting to boil outdissolved carbon dioxide gas from the solution in said member, saidmember conducting said gas back to said tank, said member also servingto transfer warmed solution therein back into said tank, means forventing carbon dioxide gas `from the tank, and means for reducing the owof solution into the member comprising a movable plug for said open endportion. j

7. A constant low temperature bath comprising a bath liquid which is tobe maintained at a constant temperature below room temperature, a singlehollow member of heat conducting material extending into the bath liquidin heat exchange relationship therewith, said member having asubstantially vertical disposition in said bath liquid, a reservoir fora low boiling solvent for carbon dioxide adjacent the upper end of themember, said member having a short open end portion thereof whichextends into said reservoir and terminates adjacent the oor -of thelatter, the other end of said member being closed and extending into andterminating in said bath liquid, said reservoir being adapted to holdsolid carbon dioxide resting in the solvent and serving to cool thesame, a portion of said carbon dioxide dissolving in the solvent, saidcooled Solvent and dissolved carbon dioxide being adapted to flow bygravity from the reservoir into the member and thereby cool the bathliquid, the heat of the bath liquid `acting to boil out dissolved carbondioxide from the solvent and said member conducting the carbon dioxidegas to said reservoir, and said member in turn being automaticallyrellable by colder solvent from the reservoir.

8. In a constant temperature bath comprising a bath liquid, theimprovement comprising |a supply of cold heat transfer medium in thenon-gaseous phase adjacent said bath liquid, said medium being a gas atbath temperatures, a supply of solvent for said medium in contacttherewith and forming a solution of the same, Ka heat transfer memberextending into the bath liquid for vertical disposition therein, saidmember having an open end portion extending into said solution forreceiving the same and a closed end portion disposed in said bathliquid, the solution being adapted to ow in said member to cool down thebath liquid by heat exchange therewith, said solution being out ofContact With the bath liquid, said member `also serving to transfermedium therein in the reverse direction back to said supply, and meansfor reducing the ow of solution into the member, comprising a plug forsaid opend end portion of said member.

9. The bath of claim 8 wherein said cold heat transfer medium is in thes-olid phase.

10. The bath of claim 8 wherein said cold heat transfer medium is in theliquid phase.

11. In a constant temperature bath comprising a bath liquid, theimprovement comprising a source of supply of cold heat transfer mediumin the liquid phase adjacent said bath liquid, said medium being a gasat 'bath temperatures, a heat transfer member extending into the bathliquid and having an end portion which terminates therein, the other endportion of said member extending into said supply source for permittingow of said liquid medium therein, the liquid medium being adapted toflow in said member to cool down the bath liquid by heat exchangetherewith, said member also serving to transfer liquid medium therein inthe reverse direction back to said supply source, and means for reducingthe flow of liquid medium into the member.

12. A constant low' temperature bath comprising a bath liquid, a walledcontainer of cold heat transfer medium in the non-gaseous phase adjacentsaid bath liquid, said medium being a gas at bath temperatures, a supplyof solvent for said medium in contact therewith and forming a solutionof the same on the floor of the container, a heat transfer memberextending from the container into the bath liquid and having a shortopen end portion thereof which extends into said container andterminates adjacent the door thereof, said open end portion permittingow -of said solution therein, the solution being adapted to flow in saidmember to cool down the bathY liquid by heat exchange therewith, meansfor venting gaseous medium from the container, means comprising a plugon said open end portion for reducing the ow of solution into themember, and said flow-reducing means being attached to a wall of saidcontainer andV being manually operable.

References Cited by the Examiner UNITED STATES PATENTS 1,989,247 1/35Rooney 62-384 2,096,088 10/37 Copeman 62-386 2,437,332 3/48 Newton62-387 2,445,294 7/48 Nelson 62-384 2,580,210 12/51 Zukerman 62-1652,674,859 4/54 Koch 62-387 MEYER PERLIN, Primary Examiner.

ROBERT A. OLEARY, Examiner.

1. A CONSTANT LOW TEMPERATURE BATH COMPRISING A BATH LIQUID WHICH IS TOBE MAINTAINED AT A CONSTANT TEMPERATURE BELOW ROOM TEMPERATURE, A HOLLOWMEMBER OF HEAT CONDUCTING MATERIAL EXTENDING INTO THE BATH LIQUID INHEAT EXCHANGE RELATIONSHIP THEREWITH, A RESERVOIR FOR A COOLANT INCOMMUNICATION WITH THE MEMBER, SAID COOLANT BEING ADAPTED TO FLOW FROMTHE RESERVOIR INTO THE MEMBER AND THEREBY COOL THE BATH LIQUID, MEANS TOREDUCE THE FLOW IN THE MEMBER, AND MEANS IN THE BATH LIQUID